M. Blaszczyszynowa et al., ADSORPTION OF H2O ON PT FIELD EMITTER - SURFACE-DIFFUSION AND FIELD-INDUCED EFFECTS, Acta Physica Polonica. A, 88(3), 1995, pp. 511-526
Adsorption of an H2O layer onto a Pt field emitter tip under the influ
ence of an electric field and the surface diffusion of water were stud
ied by using the field electron microscopy method. The presence of a n
egative field (field electron microscopy mode of operation), examined
in the range of 33-44 MV/cm, significantly reduced tile water coverage
on the emitter at temperatures above 120 K. The reduction could also
occur upon drawing a high density field emission current when the emit
ter was kept at 78 It. Surface diffusion of water, which was observed
in the temperature range 120-132 K, corresponded to the ''unrolling th
e carpet'' mechanism and started from a water multilayer to a surface
region water- and/or hydrogen-submonolayer covered. This was accompani
ed by the transition process from the state of the current- and field-
induced redistribution of H2O to the state of thermal equilibrium. Til
e activation energy of the diffusion was found to be 19 and 25 kJ/mol
depending on the crystallographic direction. A positive electric field
of 44 MV/cm, which was applied at temperatures of the substrate in ex
cess of 121 It, decreased the field emission of the system and raised
the desorption temperature of the layer over 720 It. It is assumed tha
t the negative electric field causes reorientation of H2O molecules at
the surface of platinum tip. The positive as well as negative electri
c fields promote the field desorption of water, which is in accordance
with the results reported before.